The advent of information communication technology is rapidly changing the form of data storage from an analog format to a high-quality digital format which is easily adaptable to further processing. The importance of digital information is increasing, especially in the area of computer graphics, digital library, cyber magazines and cyber space communications. Among various digital informations, text and still-picture information are widely traded in the virtual market through the Internet, which allow easy and extensive distribution of the information throughout the world. Transmission of audio and video information through the Internet is increasing at an exponential rate as the media for audio and video transmission proliferates.
However, there are problems associated with the rapid distribution and dissemination of the information. One of the problems are the proliferation of the unauthorized copying and illegal distribution of copyrighted digital material. This problem is compounded by the fact that the multimedia digital information of text, image, video, and sound can be easily mass-duplicated in exact copies.
Infringement of intellectual property rights by copying and distributing digital information in the virtual space is rapidly growing. Various protection measures are being developed to protect the intellectual property rights of the owners from unauthorized copying and distribution. Currently developed protection measures include encryption, digital watermarking, and system security. The present invention is concerned with watermarking of digital images.
Watermarking (or digital signature) is a method developed to protect information by embedding additional information into the original information to be protected. Watermarking may be classified into visible watermarking and invisible watermarking. (See J. J. K. Ruanaidh, F. M. Boland and O. Sinnen, 1996, “Watermarking Digital Images for Copyright Protection”, EVA).
Visible watermarking adds copyright notice and information to the original information. It is illegal to remove the notice and illegal to copy without the author's permission. But preservation of the copyright notice and prevention against illegal copying is very difficult against infringement and illegal copying. Invisible watermarking designed to indicate ownership can prevent illegal erasure of the watermark by third parties without impairing the original information. But there is a problem of image distortion in the information produced by the conventionally available watermarking processes according to the known prior art. Thus, there is a compelling need for an improved watermarking method to overcome the foregoing and related problems.
Watermarking (or digital signature) is a method used to mark the proprietary ownership by means of copyright notice, logo or trademark and identify unauthorized copying and distribution of copyrighted material. The watermarking is accomplished by inserting “marks” which is not visible to the naked eye on the information sought to be protected. Extensive research has been underway in many industrialized countries around the world to provide an improved watermarking method. This research effort has been intensified for the following reasons. Enabled by the emerging digital technology increasingly various media, such as newspapers, magazines, library, electronic museum, video-on-demand, audio-on-demand, MP3, web site, TV, digital radio, and certification of public documents, crdit checking transaction, transmittal of monetary and security information, has gone digital. The digital technology is bringing a form of revolution and this is even further heightened by Internet, Internet TV, digital YV, MP3 and so on.
The technologies developed to date for watermarking include the spatial method, the frequency domain method, and the spread spectrum method. The spatial method has the advantage that the watermark can be added easily, but has the disadvantage in that the image or information being watermarked and the image itself is susceptible to distortion as it is subjected to lossy compression and filtering. (See G. C. Langelaar, J. C. A. van der Lubbe and J. Biemond, 1998, “Copy Protection for Multimedia Data based on Labeling Techniques”; H. Berghel, and L. O'GorMan, 1998, “Digital Watermarking”; Aura T., “Practical invisibility in digital communication”, 1998; O. Bryndonckx, J.-J. Quisquater and B. Marcq, 1998, “Spatial Method for Copyright Labeling of Digital Images.”)
The frequency domain method converts the digital data into the analog signals of frequency components, and inserting a watermark using various transform techniques, such as DCT, FFT or wavelet transforms. Although the watermark created by the frequency domain method is difficult to erase because it is distributed over the entire data, there is the problem of image distortion depending on the values of the coefficients. (See Peticolas, F. A. P., R. J. Anderson and M. G. Kuhn, 1998, “Attacks on copyright marking systems”; Cox, I. J., J. Kilian, T. Legithton and T. Shamoon, 1996, “Secure Spread Spectrum Watermarking for Images, Audio and Video”, Proc. International Conference on Image Processing. ICIP '96. Vol. III. Pp. 243–246; Wolfgang, R. B. and E. J. Delp, 1996, “A Watermarking for Digital Images”, proceedings of the 1996 International Conference on image processing, Lausanne, Switzerland, vol. 3, pp. 219–222; M. Ejima, A. Miyazaki, and T. Saito, 1998, “Digital Watermark based on the Dyadic Wavelet Transform and its Robustness on Image Compression”, Proceedings of ITC-CSSSS '98, Sokcho, Korea, pp. 125–128).
The spread spectrum method which has become popular in recent years. Here the watermark is spread over the audio or the digital image during the DCT (discrete cosine transform) process based on the spread spectrum method. During this process, the spectrum is analyzed and n number of high coefficients, that is, the important portions of the spectrum, are modified. This method is similar, in part, to the frequency domain method. This method also utilizes the CDMA technique, in part, by spreading the watermark broadly. This method avoids impairment of the watermark somewhat in the transform processes, that is, in JPEG, copying, scanning, scaling compression/expansion processes. But this method causes the watermark to suffer in the data compression stage, that is, the watermark is considerably impaired in the data compression stage.